1. Field of the Invention
The present invention relates in general to ballast cases for electronic fluorescent lamps and, more particularly, to a structural improvement in such ballast cases for facilitating the potting compound charging work, which potting compound is typically charged in the ballast case with the object of protection of the ballast as well as of prevention of noise.
2. Description of the Prior Art
As well known to those skilled in the art, a typical ballast case for electronic fluorescent lamp comprises a ballast enclosure and a cover. The ballast enclosure of the ballast case supports the ballast and varieties of parts therein and is charged with potting compound for protection of both the ballast and varieties of parts. The ballast enclosure charged with the potting compound is assembled with the cover, thus to form the ballast case.
With reference to FIGS. 1 and 2, there is shown a typical ballast case designated by the numeral 10. The ballast enclosure 12 of the ballast case 10 has a rectangular box shape, while the cover 14 covering the ballast enclosure 12 is a rectangular plate.
That is, the ballast enclosure 12 of the ballast case 10 is installed with the ballast (S) itself and varieties of parts (P) therein as best seen in FIG. 2. The ballast enclosure 12 installed with the ballast (S) and varieties of parts (P) is, thereafter, charged with the potting compound (C) for protecting both the ballast (S) and varieties of parts (P). The ballast enclosure 12 in turn is covered with the cover 14, thus to form the ballast case 10.
With the potting compound (C) charged in the ballast enclosure 12 installed with the ballast (S) and varieties of parts (P), the ballast (S) and varieties of parts (P) are effectively protected. Furthermore, the potting compound (C) prevents the noise generated from both the ballast (S) and varieties of parts (P). When the ballast enclosure 12 is charged with deficient amount of potting compound (C), there will be formed a cavity in the ballast enclosure 12 and such a cavity causes a problem that prevention of noise as well as protection of parts can not be achieved. Therefore, charging of potting compound (C) in the ballast enclosure 12 should be carried out with prudence. In order to achieve the desired protection of both the ballast (S) and varieties of parts (P) along with the desired prevention of operational noise of the ballast, the potting compound (C) should be charged in the ballast enclosure 12 so that a potting compound layer is formed between the top surface of the ballast (S) and the bottom surface 14a of the cover 14. In order to achieve the above object, a sufficient amount of potting compound (C) should be charged in the ballast enclosure 12 so that the potting compound (C) completely covers the top surface of the ballast (S) and hides the ballast (S). In this case, the potting compound (C) not only prevents noise generation by absorbing the vibration caused by overvoltage of the ballast (S) but also protects the ballast (S) and the parts (P).
However, a potting compound charging worker who is anxious about overflow of the sticky potting compound (C) out of the ballast enclosure 12 often charges deficient amount of potting compound (C) in the ballast enclosure 12 during manufacture of the ballast cases 10. When deficient amount of potting compound (C) is charged in the ballast enclosure 12 so that the potting compound Can not cover the top surface of the ballast (S), there is formed a cavity 16 between the top surface of the ballast (S) and the bottom surface 14a of the cover 14 as shown in FIG. 2. The cavity 16 causes the overvoltage of the ballast (S) to be sent through the cavity 16, thus to generate severe noise.